[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Qemu-devel] [patch] IDE busmaster DMA support

From: John Coiner
Subject: [Qemu-devel] [patch] IDE busmaster DMA support
Date: Mon, 26 Sep 2005 21:48:25 -0400
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.11) Gecko/20050731


Here's another patch to enable IDE DMA:


This patch, like Juergen Lock's earlier patch from which it is derived, replaces the virtual PIIX3 IDE controller with a PIIX4.

It applies cleanly to 0.7.2.

This patch extends the Windows 2000 install hack to work for DMA also -- I installed and ran Windows 2000 with DMA enabled.

It'd be cool if QEMU supported nonblocking disk access -- if it would let the guest resume running currently, while waiting for the disk to finish seeking. This patch is a first step toward concurrent IO, which would probably have to use busmastering DMA transfers to be efficient, if it's going to be efficient at all.

Do people have ideas about how to implement concurrent IO? I have a couple hazy ideas...

Can anyone shed light on the potential performance to be realized? For example, how long does a context switch take in the guest? If it takes 10ms (one disk seek) then there's probably no benefit to concurrent disk IO. If a context switch takes 1ms, then the guest has opportunity to make forward progress while awaiting an IDE interrupt.

Regards, happy hacking,


reply via email to

[Prev in Thread] Current Thread [Next in Thread]